As feature sizes continue to decline in modern photolithographical semiconductor manufacturing processes, effects, such as undesired line edge roughness, insufficient lithographical resolution, and limited depth of focus problems can increase. More particularly, photoresist image footprints may become increasingly difficult to control as semiconductor device features become smaller and closer together.
Adhesion promoters may be used to bond the photoresist to the semiconductor substrate or other device surface until the photoresist is exposed to light, thereby defining feature edges and boundaries within the device. Photoresist, however, may persist around the substrate surface and photoresist interface. This is because some regions toward the bottom of the photoresist may not become sufficiently soluble after being exposed to an incident radiation to be completely removed, and instead remain bonded to the substrate by the adhesion promoter. These areas of persisting photoresist may correspond to areas where an incident radiation signal is weakest due to radiation absorption by photoresist or reflective interaction effects between the substrate and photoresist.
FIG. 1 illustrates a prior art adhesion promoter. The adhesion promoter of FIG. 1 is a Hexamethydisilyazide (HMDS) adhesion promoter and serves to help bond the photoresist layer to the underlying substrate. Accordingly, the adhesion promoter is removed along with the photoresist after being exposed to incident radiation.
FIG. 2 illustrates a prior art process for forming an adhesion promoter and photoresist layer on a semiconductor substrate. The prior art adhesion promoter of FIG. 1 is applied to a semiconductor substrate, followed by a photoresist layer being applied superjacent to the adhesion promoter. A mask layer is applied, exposing the photoresist layer to incident ultra-violet light in areas that are not covered by the mask layer. These process steps may also be applied to other layers of a semiconductor die.
The result of the above-described process step can be illustrated by the example of FIG. 3. FIG. 3 is a photograph of a line-spacing pattern illustrating roughness and poorly defined edges associated with a typical photoresist removal process. Particularly, FIG. 3 illustrates photoresist deposits persisting between device features after being exposed to an incident radiation, such as ultra-violet light.